What is the difference between an ovulatory cycle and an anovulatory cycle in a clinical context?

From the Guidelines

The key difference between ovulatory and anovulatory cycles is that ovulatory cycles involve the release of an egg from the ovary, while anovulatory cycles do not, with the most recent evidence suggesting that anovulatory cycles are often associated with polycystic ovary syndrome (PCOS) and other endocrine disorders 1. In a normal ovulatory cycle, follicular development progresses through distinct phases: follicular phase with menstruation and follicle growth, ovulation when LH surge triggers egg release, and luteal phase when the corpus luteum produces progesterone. This results in regular, predictable menstrual cycles with biphasic basal body temperature patterns and mid-luteal progesterone levels above 3 ng/mL. Some key points to consider in the diagnosis and management of ovulatory and anovulatory cycles include:

• Common causes of anovulatory cycles include PCOS, hypothalamic dysfunction, hyperprolactinemia, thyroid disorders, and extremes of reproductive age 1
• Clinical significance is substantial as anovulation causes infertility and increases risk of endometrial hyperplasia due to unopposed estrogen
• Diagnosis involves menstrual history, physical examination, basal body temperature tracking, serum progesterone measurement, and sometimes ultrasound monitoring
• Treatment depends on the underlying cause and patient goals, ranging from lifestyle modifications to medications like clomiphene citrate or letrozole for those seeking pregnancy, with recent guidelines suggesting the use of progestin-only contraception and combined hormonal contraception for abnormal uterine bleeding associated with ovulatory dysfunction 1. It is essential to note that the evaluation and management of reproductive endocrine disorders in women with epilepsy require close cooperation between neurologists and endocrinologists or gynaecologists, as these specialists may not have a detailed understanding of the effects of epilepsy or antiepileptic drugs on the endocrine system 1.

From the FDA Drug Label

Clomiphene citrate is indicated for the treatment of ovulatory dysfunction in women desiring pregnancy. A basal body temperature graph or other appropriate tests may help the patient and her physician determine if ovulation occurred. Following ovulation, plasma progesterone and estradiol rise and fall as they would in a normal ovulatory cycle

The main difference between an ovulatory cycle and an anovulatory cycle is the presence or absence of ovulation.

• An ovulatory cycle is characterized by the release of an egg from the ovary, which is typically accompanied by a preovulatory gonadotropin surge and subsequent follicular rupture.
• An anovulatory cycle, on the other hand, is a cycle in which ovulation does not occur, and is often associated with hormonal imbalances and infertility. In a clinical context, the distinction between ovulatory and anovulatory cycles is crucial for the diagnosis and treatment of ovulatory dysfunction and infertility 2, 2.

From the Research

Definition of Ovulatory and Anovulatory Cycles

• An ovulatory cycle is a menstrual cycle in which ovulation occurs, resulting in the release of an egg from the ovary [(3,4,5)].
• An anovulatory cycle, on the other hand, is a menstrual cycle in which ovulation does not occur, and no egg is released [(3,4,5)].

Clinical Characteristics

• Women with anovulatory cycles tend to have higher levels of androgens, such as testosterone, and a higher free androgen index compared to those with ovulatory cycles [(3,4)].
• Anovulatory cycles are often associated with longer menstrual cycle lengths and a higher incidence of amenorrhea 3.
• Ovulatory cycles, in contrast, are typically characterized by regular menstrual cycles and lower levels of androgens [(3,4)].

Response to Treatment

• Women with ovulatory cycles tend to respond better to ovulation induction treatment with clomiphene citrate, with a higher likelihood of achieving regular menstrual cycles 3.
• In contrast, women with anovulatory cycles may require more aggressive treatment, such as recombinant FSH, to achieve pregnancy 3.

Prevalence of Anovulation

• Studies have shown that anovulation can occur in up to 37% of clinically normal menstrual cycles 5.
• Anovulatory cycles can be associated with a range of symptoms, including menstrual cramps, which can be more severe in anovulatory cycles 6.

Hormonal Differences

• The hormonal profile of ovulatory and anovulatory cycles differs, with ovulatory cycles characterized by a mid-luteal phase progesterone surge and anovulatory cycles lacking this surge [(4,5)].
• The pituitary response to GnRH also differs between ovulatory and anovulatory cycles, with a more normal response observed after an ovulatory cycle 7.